Colloidal aggregation phenomena: Spatial structuring of TEOS-derived silica aerogels

In this contribution. the homogeneity of silica aerogels made from tetraethyl orthosilicate (TEOS) was Studied by means of Fourier transform infrared (MR) and Si-29 nuclear magnetic resonance (NMR) spectroscopies. FTIR spectra show a slight difference in the asymmetric Si-O-Si stretching vibration frequency in the outer and inner part of the aerogels. According to the Si-29 NMR data, a higher relation Q(4)/Q(3) was obtained in the inner parts of the gels compared with their outer parts, proving the difference in the cross linkage of the silica network. The obtained results are interpreted in terms of the specific spatial Structuring of the colloidal suspensions due to the presence of gravity. (c) 2005 Elsevier Inc. All rights reserved.